The present invention generally relates to an electrical resonator and more particularly, to a coaxial resonator for use in an electrical filter or oscillator to be applied, for example, to UHF ranges.
With respect to coaxial resonators to be used for electrical and electronic equipment which operate, for example, in UHF ranges, it has been a recent trend that a 1/4 wavelength coaxial resonator (referred to as a .lambda./4 coaxial resonator hereinbelow) compact in size and composed of a dielectric member having a high unloaded Q begins to be adopted. However, by the coaxial resonator as described above alone, its resonance frequency can not be readily altered, thus requiring much time for the adjustments thereof. Accordingly, it is so arranged in some cases, that a trimmer capacitor or the like is added to the coaxial resonator for making it possible to readily alter the resonance frequency, but in this case, there have been such disadvantages that the size of the coaxial resonator tends to be increased, while the high unloaded Q which is an essential feature of the .lambda./4 coaxial resonator employing the dielectric member is undesirably lowered.
In FIG. 1, there is shown one example of the conventional arrangements as referred to above, in which a coaxial resonator 2 constituted by the cylindrical dielectric member, and having electrode layers formed on inner and outer peripheral surfaces and also on one end face of the dielectric member by a metallizing process or the like, is mounted on a printed circuit board 1, while a trimmer capacitor 3 is disposed in the vicinity of the coaxial resonator 2, with a ground terminal 4 of the trimmer capacitor 3 being connected to the electrode formed on the inner peripheral surface of the coaxial resonator 2.
The known arrangement as described above, however, still has drawbacks in that, since the ground terminal 4 of the trimmer capacitor 3 is prolonged to be connected to the electrode on the inner peripheral surface of the coaxial resonator 2, an electrical loss tends to be produced depending on the length of the ground terminal 4, thus resulting in deterioration of unloaded Q, while addition of the completely independent trimmer capacitor 2 and also necessity for employing the printed circuit board 1 give rise to increase of the number of parts involved, with consequent rise in cost and economical disadvantage.